This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A168674 #23 Sep 08 2022 08:45:49
%S A168674 0,4,6,12,20,34,56,92,150,244,396,642,1040,1684,2726,4412,7140,11554,
%T A168674 18696,30252,48950,79204,128156,207362,335520,542884,878406,1421292,
%U A168674 2299700,3720994,6020696,9741692,15762390,25504084,41266476,66770562,108037040
%N A168674 a(n) = 2*A001610(n).
%C A168674 This sequence has a golden mean ratio limit.
%H A168674 G. C. Greubel, <a href="/A168674/b168674.txt">Table of n, a(n) for n = 0..1000</a>
%H A168674 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2, 0, -1).
%F A168674 a(n) = 2*a(n-1) - a(n-3). [Dec 03 2009]
%F A168674 G.f.: 2*x*(2 - x)/((1-x)*(1 -x -x^2)). [Dec 03 2009]
%t A168674 M = {{0, 1}, {1, 1}} v[0] = {0, 1}; v[n_] := v[n] = M.v[n - 1] + {3, 2} a = Table[v[n][[1]], {n, 0, 30}]
%t A168674 LinearRecurrence[{2, 0, -1}, {0, 4, 6}, 60] (* _Vladimir Joseph Stephan Orlovsky_, Feb 10 2012 *)
%t A168674 RecurrenceTable[{a[0] == 0, a[1] == 4, a[2] == 6, a[n] == 2 a[n-1] - a[n-3]}, a, {n, 50}] (* _Vincenzo Librandi_, Jul 30 2016 *)
%o A168674 (Magma) I:=[0,4,6]; [n le 3 select I[n] else 2*Self(n-1)-Self(n-3): n in [1..40]]; // _Vincenzo Librandi_, Jul 30 2016
%o A168674 (PARI) a(n)=([0,1,0; 0,0,1; -1,0,2]^n*[0;4;6])[1,1] \\ _Charles R Greathouse IV_, Jul 30 2016
%Y A168674 Cf. A022087, A019274, A006355, A001610.
%K A168674 nonn,easy
%O A168674 0,2
%A A168674 _Roger L. Bagula_ and _Gary W. Adamson_, Jun 01 2010
%E A168674 Definition simplified and notation in formulas set to OEIS standards by the Assoc. Editors of the OEIS, Dec 03 2009